Inspection Procedure 21
INSPECTION PROCEDURE 21: Power supply system and ignition switch - IG system.
CIRCUIT OPERATION
- Battery positive voltage is applied to the MFI relay (terminals No. 3, No.
4).
- When the ignition switch is turned to the "ON" position, battery positive voltage is applied to the ECM (terminal No. 92). When battery positive voltage is applied, the ECM turns the power transistor in the ECM "ON" and grounds the MFI relay coil. With this, the MFI relay turns "ON" the battery positive voltage is supplied to the ECM (terminals No. 82) from the MFI relay (terminal No. 2).
- A battery positive voltage is constantly supplied to the ECM (terminal No. 104) as the backup power.
- The ECM (terminals No. 81, No. 93) is grounded to the vehicle body.
COMMENT
- When the ignition switch "ON" signal is input into the ECM via ETACS-ECU, the ECM turns "ON" the MFI relay. This causes battery positive voltage to be supplied to the ECM, sensor and actuator.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Malfunction of the ignition switch.
- Malfunction of the MFI relay.
- Improper connector contact, open circuit or short-circuit harness wire.
- Malfunction of the ECM.
DIAGNOSIS
STEP 1. Check harness connector A-33X at MFI relay and harness connector B-11 at ECM for damage.
Q. Is the connector in good condition?
YES Go to Step 2.
NO Repair or replace it. Harness Connector Inspection.
Then confirm that the malfunction symptom is eliminated.
STEP 2. Check the MFI relay.
(1)Remove the MFI relay.
(2)Check for continuity between the MFI relay terminals No. 1 and No. 3.
- There should be continuity.
(3)Use jumper wires to connect MFI relay terminal No. 3 to the positive battery terminal and terminal No. 1 to the negative battery terminal.
(4)Check for continuity between the MFI relay terminals No. 2 and No. 4 while connecting and disconnecting the jumper wire at the negative battery terminal.
- Should be less than 2 ohms. (Negative battery terminal connected)
- Should be open loop. (Negative battery terminal disconnected)
(5)
Install the MFI relay.
Q. Is the measured resistance within the specified range?
YES Go to Step 3.
NO Replace the MFI relay. Then confirm that the malfunction symptom is eliminated.
STEP 3. Measure the power supply voltage at MFI relay harness side connector A-33X.
(1)Disconnect the connector A-33X and measure at the harness side.
(2)Measure the voltage between terminals No. 3, No. 4 and ground.
- Voltage should be battery positive voltage.
Q. Is battery positive voltage (approximately 12 volts) present?
YES Go to Step 4.
NO Repair harness wire between fusible link (36) and MFI relay connector A-33X (terminal No. 3, No. 4) because of open circuit. Then confirm that the malfunction symptom is eliminated.
STEP 4. Measure the ignition switch-IG signal voltage at ECM harness side connector B-11.
(1)Disconnect the connector B-11 and measure at the harness side.
(2)Turn the ignition switch to the "ON" position.
(3)Measure the voltage between terminal No. 92 and ground.
- Voltage should be battery positive voltage.
(4)Turn
the ignition switch to the "LOCK" (OFF) position.
Q. Is battery positive voltage (approximately 12 volts) present?
YES Go to Step 5.
NO Check harness connectors C-304 and C-317 at intermediate connector for damage, and repair or replace as required. Refer to Harness Connector Inspection Harness Connector Inspection.
If intermediate connectors are in good condition, repair harness wire between ignition switch connector C-210 (terminal No. 2) and ECM connector B-11 (terminal No. 92) because of open circuit.
Then confirm that the malfunction symptom is eliminated.
STEP 5. Measure the backup power supply voltage at ECM harness side connector B-11.
(1)Disconnect the connector B-11 and measure at the harness side.
(2)Measure the voltage between terminal No. 104 and ground.
- Voltage should be battery positive voltage.
Q. Is battery positive voltage (approximately 12 volts) present?
YES Go to Step 6.
NO Repair harness wire between relay box (fuse 2) and ECM connector B-11 (terminal No. 104) because of short circuit. Then confirm that the malfunction symptom is eliminated.
STEP 6. Check for continuity at ECM harness side connector B-11.
(1)Disconnect the connector B-11 and measure at the harness side.
(2)Check for the continuity between terminals (No. 81, No. 93) and ground.
- Should be less than 2 ohms.
Q. Does continuity exist?
YES Go to Step 7.
NO Check harness connector A-66 at intermediate connector for damage, and repair or replace as required. Harness Connector Inspection.
If intermediate connector is in good condition, repair harness wire between ECM connector B-11
(terminal No. 81, No. 93) and ground because of open circuit and harness damage. Then confirm that the malfunction symptom is eliminated.
STEP 7. Measure the power supply voltage at ECM harness side connector B-11.
(1)Disconnect the connector B-11 and measure at the harness side.
(2)Measure the voltage between terminal No. 73 and ground.
- Voltage should be battery positive voltage.
Q. Is battery positive voltage (approximately 12 volts) present?
YES Go to Step 8.
NO Repair harness wire between MFI relay connector A-33X (terminal No. 1) and ECM connector B-11 (terminal No. 73) because of open circuit. Then confirm that the malfunction symptom is eliminated.
STEP 8. Check for open circuit and harness damage between MFI relay connector A-33X (terminal No. 2) and ECM connector B-11 (terminal No. 82).
(1)Disconnect the connector A-33X and B-11 measure at the harness side.
(2)Measure the resistance between connector A-33X (terminal No. 2) and connector B-11
(terminal No. 82).
- Should be less than 2 ohms.
Q. Is the harness wire in good condition?
YES Replace the ECM. When the ECM is replaced, register the ID code. Refer to ID registration procedure manual - ID codes registration judgement table [Vehicles with KOS] or ID registration procedure manual - ID codes registration judgement table [Vehicles with WCM]. Then confirm that the malfunction symptom is eliminated.
NO Repair it. Then confirm that the malfunction symptom is eliminated.